This is a two-step study, with each step lasting 24 weeks. Step 1 is double-blind and Step 2 is open label. At entry, patients are randomly assigned to receive either the STS or placebo. One STS patch will be applied daily at the same time for 24 weeks. Patients are evaluated at the clinic at entry and at Weeks 2, 4, 8, 12, 16, and 24. Cognitive status will be evaluated by performance on a series of neuropsychological assessments. Patients who complete Step 1 may participate in Step 2. Patients on placebo in Step 1 will receive active STS treatment in Step 2. The STS patch is applied once daily for an additional 24 weeks and patients are evaluated at the clinic at Weeks 28, 36, and 48.